Technical Field
The present disclosure relates to a power conversion apparatus that includes a power conversion circuit that converts electric power through operation of a plurality of switching elements.
Related Art
Conventionally, regarding power conversion apparatuses that include a power conversion circuit, such as a boost converter or an inverter, a technology is known in which output limitation is applied to the power conversion circuit when the highest temperature of the temperatures of a plurality of switching elements reaches a predetermined temperature or higher. Hereafter, element refers to the switching element, unless otherwise noted. In addition, the temperature of the element that has the highest temperature among the plurality of elements is abbreviated and referred to as highest element temperature.
For example, in a motor drive apparatus disclosed in JP-A-2007-195343, a temperature detection diode and a temperature monitor circuit are provided for one of six elements configuring an inverter circuit. In addition, a temperature detection diode and a temperature detection circuit are provided for each of the remaining five elements that are not provided with the temperature monitor circuit. The temperature detection circuit detects that the element temperature has reached a predetermined temperature.
A controller serves as a temperature estimating means. The controller adds, to a monitored temperature detected by the temperature monitor circuit, a value read out from map data generated based on a model of heat transfer among a plurality of switching elements, and thereby estimates a highest element temperature estimated value. In addition, when it is detected that the temperature of any of the elements provided with the temperature detection circuit has reached a predetermined temperature, the controller sets, as a correction value, the difference between the highest element temperature estimated value and the predetermined temperature. The controller adds the correction value to the highest element temperature estimated value, and sets the sum as a post-correction highest element temperature estimated value.
The heat transfer model used in the apparatus disclosed in JP-A-2007-195343 is prescribed taking into consideration thermal interference between elements that are arranged adjacent to each other in the element arrangement on a substrate, and the like. However, reliability of the heat transfer map data may decrease due to deterioration of inter-element heat transfer characteristics and the like. The highest element temperature may not be accurately estimated.
In addition, variable factors in the element temperatures acquired by the temperature estimating means are present in actuality. The factors include, for example, output error in the temperature detection diode, detection error in the temperature monitor circuit and the temperature detection circuits, variations in characteristics among the plurality of elements, and external disturbances. However, the conventional technology in JP-A-2007-195343 focuses only on the highest element temperature and gives no consideration to such variations.
Therefore, from the perspective of reliably protecting the elements from overheating, an output limitation temperature is required to be set with the addition of a safety margin that provides allowance taking into account the entirety of the various variable factors. Consequently, excessive output limitations tend to be applied. Element performance cannot be effectively realized. As a result, the overall apparatus may become larger in size due to higher-specification switching elements and larger circuit scale.